Here Im mostly asking about PC games, as the full 3d era in console gaming was pretty much started with the PS1 launch (December 1994) and the N64 launch (September 1996).
Case in point is two of my favourite games, Star Wars Dark Forces (February 1995), and Dark Forces 2 (October 1997), pretty much the same formula, but totally different technical capabilities.
Dark Forces was solidly lumped in with the Doom era of games, being 2.5D. Basically the environment was 3D, enemies were rendered by a 2d billboard sprite, and for Dooms case, all levels were essentially on a 2D grid, with the appearance of raised ceilings and uneven floors essentially kludged into the engine. Dark Forces slightly expanded on this by somehow adding in the ability to have multiple levels (is it only 2 different vertical levels or more?) and the ability to pan looking up and down ([although this again seems to have been a hotfix to an inherent issue in raycasting engines](https://en.wikipedia.org/wiki/File:Camera_Rotation_vs_Shearing.gif)).
So then a little under 3 years later Dark Forces 2 is released by the same publisher, you can do pretty much everything you can in a normal game engine, look in any direction, completely 3d environments, and the graphics still look passable even now.
I get that there are some technical hurdles to cover between 2D games and full 3D, particularly without a graphics card (first hitting the market in 1999) to reduce the performance issues with rendering only what is in view (occlusion I think?). What I dont get is how the technical issues were solved so quickly between 1995 and 1997, and in particular why the 2d grid necessity went away so quickly.
In: Technology
There is a “beautiful” algorithm called ray casting which is at the heart of many “2.5d games”. There was a period in time where ray casting was the most effective way to do real time 3d with textures. It started becoming popular 1992 (Wolfenstien), and was uncommon around 1998. With Moores law, there was about an 8 fold increase in computing power in that period. There also happened a massive improvement in floating point computation capacity during this time. This meant the end to the niche where ray casting was relevant.
If you wan’t to know about the algorithm [https://permadi.com/1996/05/ray-casting-tutorial-table-of-contents/](https://permadi.com/1996/05/ray-casting-tutorial-table-of-contents/)
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